[FoxHunt] Moded ELTS

[Kuon & Dale Hunt]

>-Here in Yamhill County, Oregon, we got some old ELT beacons and
>-recrystalled them for
>-121.775......
>
>
>Great!  Go for it Dale.
>
>One thing to check is to see if your ELT is radiating strong RF on the
>second harmonic. .....


     We paid attention to that in the conversion.  One box has an outboard
     low pass filter with BNC connectors that goes in line with the antenna.
     In another we replaced the output circuit with a low-pass "T" network.

     Fortunately, we have access to a spectrum analyzer, and made good use
     of it!  We have also reduced the power output a bit.

     The ELTs we converted are probably similar to many - the modulation is
     applied in the collector lead one or two stages away from the final
     (to minimize the amount of audio power required, and perhaps to
     broaden the signal to make it easy to hear!)  An AM signal
     amplified by one or two class-C stages is going to splatter all over
     the band!  So one of the future projects will be to clean up the
     modulation and keep it within a reasonable bandwidth (+/- 10 kHz or
     so.)  Unmodified, the output at 100kHz off frequency is only down
     40dB or so, which is a big reason why 121.6 MHz didn't work well
     for a practice frequency.


     (While I was working on the other units, I repaired the practice
     beacon for the local CAP group.  Didn't look like it had ever
     worked since someone had put in the 121.775 MHz crystal, plus one
     transistor had blown, and the 1988 Radio Shack nicads were no
     longer in peak condition.)

          - Dale WB6BYU